If you assign a task to a Queue Owner, it won't work and it won't be assigned to the requestor.
I do not believe you can do what you ask because Marketo won't see the Requestor's name, it just sees Lead Owner. So even if you created a custom field to capture Lead Owner name, you couldn't do that with Requestor or "Current User".
But, if you know someone who is skilled at Apex code, it might be possible to capture that Requestor name and put it in a custom field and pass it along with the Lead record during the campaign process.
Last MSI Requestor=Current User Action Name
It might be better to have someone take ownership of the record first, then the Task can be assigned to the Lead Owner.